1. Field of the Invention
The present invention relates generally to a wavefront sensor for detecting wavefront tilts along two orthogonal directions, and more particularly pertains to a simple, white light wavefront sensor of the aforementioned type which is particularly suitable for a real-time solar image compensation system.
The field of active optics technology can be applied to high performance optical systems which encounter or are subject to random disturbances such as vibration, thermal transients or atmospheric turbulence. Active optics technology can be applied to laser beam control systems and compensated imaging systems. For instance, concerning the latter types of systems, the resolution of ground based optical imaging systems is frequently severely limited by random wavefront tilts and phase changes produced by atmospheric turbulence. The resolution of such optical systems can usually be improved considerably if the atmospheric distortion is measured and corrected in real-time before recording the image on tape or film.
2. Discussion of the Prior Art
Hardy U.S. Pat. No. 3,923,400 discloses a real time wavefront correction system of the type discussed above in which real time phase distortions in a wavefront being imaged by an optical system are detected and substantially eliminated prior to recording of the image. The Hardy wavefront correction system utilizses an AC, lateral shearing interferometer to measure in real time the relative phase differences of the wavefront. The measured phase differences are directed to an analog data processor which generates a plurality of electrical signals proportional to the required corrections at different areas of the wavefront. The electrical signals are applied to a phase corrector upon which the wavefront is incident to change the relative phase at various locations of the wavefront to achieve a wavefront in which the phase distortion is removed. The phase correction device can for instance consist of a mirror having an array of piezoelectric elements which function to selectively deform the mirror to correct phase distortions in the wavefront.
A similar type of active optics system has also been applied to an optical system for solar observations, and employs a rotating radial or Ronchi grating to detect wavefront tilts. In this prior art arrangement an array of photodetectors positioned at the conjugate image of a deformable mirror detect signals modulated by the rotating radial grating. The phase of the electrical signal at each detector is directly related to the wavefront slope at the conjugate image of the deformable mirror, and is utilized to selectively control the mirror surface in a feedback loop to null the errors. A drawback of this system is the use of relatively complex hardware having a mechanically rotating grating to modulate the wavefront prior to detection. A system of this type also requires the location of a precisely adjustable field stop in the image plane at which the rotating grating is positioned, which results in complications of both the optical and mechanical systems. Moreover, a wavefront sensor having a mechanically rotated grating is undesirable in many system applications, such as space systems and equipment requiring a compact size and a substantial tolerance to shocks and vibrations.